Aircraft are commonly provided with environmental control systems that maintain an aircraft cabin air pressure and temperature within a target range. The environmental control system receives bleed air from compressor stages of a gas turbine engine that propels the aircraft. These environmental control systems also receive bypass air that bypasses the gas turbine engine core and use this bypass air to cool the compressor air before delivery to the cabin. The bleed air and the bypass air are directed to the environmental control system through pressure lines or plenums. Some of these environmental control systems will exhaust the spent bypass air into the engine core compartment, in the vicinity of the core engine cases, in order to achieve some thrust recovery through the core compartment aft vent. This spent bypass air can have a significant cooling effect on the core engine cases. During some operational points of the aircraft, the environment control system is not used to maintain the aircraft cabin air pressure and temperature and spent bypass air is therefore not being exhausted into the vicinity of the core engine cases. It is during these operational points of the aircraft, high pressure turbine and low pressure turbine case clearances and case temperatures may need to be further controlled.
Accordingly, it is desirable to provide a system and a method to control the high pressure turbine and low pressure turbine case clearances and case temperatures when the environmental control system is not actively being used by the aircraft.